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Another TCase issue, with a twist...

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  #1  
Old 12-04-2018, 07:38 PM
pilotsmack
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Default Another TCase issue, with a twist...

Hey guys,

First off, brilliant bunch of insight on this site - glad to have found it. Tried the search function and couldn't quite find this one. Hopefully someone has some insight!

Bought na 05 Dak 4x4 4.7L for cheap. Good thing because it's had quite a few issues - mostly due to neglect by the PO. I have replaced a whole bunch of things, but this has sprung up out of nowhere and I'm at a loss.

180xxxkms, driving down the highway last week and the 4Lock and 4LO lights start flickering at 100kph (60mph), followed by the Serv 4wd light. No grinding, no sound, no jumping, didn't feel like the TC was switching. I take the next exit and slowing through 80, all the lights go away. On the way home, it does the same thing so I pull fuse 42. Get home, reader shows C1404 - diagnose the shift motor, order a new one (non-reman) from Rockauto. So far so good... except the TCase connector was hella tight - did I miss something there? Or just wedge it till it clicks?

Anyways, took it for a test. 2WD and 4Lock went back and forth no problem. Coasting down a gentle hill in N, switch to 4LO, takes a while but 4Lo engages. But now even with the switch in 4Lo, the light flashes and it is stuck in 4Lo. Tried the gentle hill in N with 4Lock selected, then 4Lo stays illuminated while 4Lock flashes. Tried switching from a stop, switching from a roll, reverse - she won't come out of 4Lo.

Got back in the garage, went to get into shop clothes, and when I came back I heard the TC motor running, even though I left the switch in 4Lo. It did this for about 20sec when I went and pulled fuse 42 again. Later, for diagnostic purposes after taking the TCMotor off again, I plugged in 42 and selected the switch to 4Lock. It does the same thing - makes noise, but doesn't actually move.

A few other articles have the FCM being the culprit when it switches with the ignition off. I don't see any corrosion or anything obvious with the FCM.

Bad replacement TC motor? Or do you guys figure something else is going on?
 
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Old 12-05-2018, 07:06 AM
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Its a short in the 5v system making the control module believe the case is in 2 gears at once so it guesses which gear it is actually in. Good luck finding it could literally be anywhere in the truck. Theres a pressure switch on the ac that tends to do it alot. After a while your t case will start actually shifting into 4low. Usually when you hit the brakes semi hard or hit a good bump. I just swapped over to a manuelly shifted np231 because of this same crap
 
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Old 12-05-2018, 11:47 AM
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Yeah, my front CV axles provide a little shake, I bet the increased vibration at higher speeds is what helps the short.

I've traced and checked the wiring according to the FSM, wires look okay as far as I can see, nothing going on with any of the connectors, even IPM connectors. At this point I'll get the motor running then likely add a switch beside the selector switch to allow power to the motor. Just to make sure it doesn't get any pant-filling ideas...

Just to clarify - the 5V signal is only for the mode sensor in the TC Motor? It won't rotate without a 12V signal?

**Sidenote: Totally agree about the electronic crap - it sucks. That's why I love that my motorcycle is carbs and monkey-mechanics**
 

Last edited by pilotsmack; 12-05-2018 at 11:52 AM.
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Old 12-05-2018, 07:10 PM
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Tbh I'm not really sure how the system works i couldnt find much info on it (which is why i ditched it rather than trying to locate the short) i know even with the fuses pulled and switch removed the plug on the case has constant power on 2 pins iirc.

I belive everything except the actual power to the motor is 5v

Edit: i just re read your first post i don't think anything I've said pretains to your situation. Misread it this morning as i was getting ready for work, being stuck in 4wd and the motor not trying to shift would be a different problem. You need to check that the shift motor is infact getting the signal to shift if it is the problem is probably the motor. If its not check the at the control module and thr switch. Having obd2 diagnostics would make it eaiser for you to find the issue tho
 

Last edited by stetson; 12-05-2018 at 07:23 PM.
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Old 12-05-2018, 08:09 PM
pilotsmack
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Yeah, followed the OBD2 diag per the FSM and it directed me to replace the motor. But the replacement was kaput so that didn't go anywhere. Since I am on-call for work at was bored sitting at home, I hooked up the OBD with live data and saw that wiggling the AC Pressure transducer made the signal go allllllllll over the place. Took it out, looked okay but I cleaned it like crazy and was very generous with the dielectric grease. Forced the TC back to 2wd and hooked up the (supposedly broken) old motor after cleaning the snot out of it and again went to town with dielectric. 45 min test trip went well, no codes, no odd voltages, though the pressure sensor seemed to return low volts (0.41-0.48V), according to the book, that's normal for the current Alberta temperature.

Thanks for the insight though, stetson! Further googling showed a service bulletin on 02-06 Rams with 4.7L V8s and RFE transmissions that the transducer was in fact problematic.

I hate the "fixed it" feeling with electronic stuff since all I really did was clean some wires. I am going to be suuuuuper paranoid for the next few weeks and will keep you guys posted, though I still intend to interrupt power to the motor so I can switch it only when I desire. By my read of the book, the mode sensor is where the 5v signal applies, and the Mode A and B signal are the return signal and the fused 12V spins the motor. This just means it's time to go back to the shop and experiment!

... tomorrow... lol
 
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Old 12-06-2018, 12:21 PM
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Kewl man glad you figured it out.
 
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Old 12-06-2018, 03:50 PM
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I hate electronic junk.

Well it did it again lol. Same conditions ,same speed. I didn't have my OBD reader with me for data, but out of curiousity, I pulled over, shut down, and pulled the harness for the AC pressure transducer. I zip-tied it out of the way, and went about my day.

Drove various conditions for a few hours and repeated the incident circumstances about a dozen times and.... no more lights!

Of course when I got home and hooked up the OBD there was a fresh C1404 for me, and the new one was a P0533 (associated with pulling the harness). I did pick and pull a few sensors, since I can't find a new part number and neither can my friends who work in parts for Chrysler. Going to do the FSM diagnoses them later to tell which ones are good and which ones are bad.

I repeat: I hate electronic junk

EDIT: One of my friends found a part number and tracked down a price: $245 CAD for JUST the transducer.... I haven't laughed that hard in a long time....
 

Last edited by pilotsmack; 12-06-2018 at 04:06 PM. Reason: lol
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